Hisako Sato

A single stereochemical inversion at the central residue of Val–Val–Ile tripeptides controls molecular packing and self-assembly pathways, producing distinct supramolecular organizations across multiple length scales.

Chirality interplay in serine-coordinated cyclometalated iridium( iii ) complexes gives rise to diastereomer-dependent emission, suggesting potential for d -serine sensing.

A chiral nanoconfined reaction field was constructed by modifying the interlayer space of a smectite clay mineral with enantiopure tris(1,10-phenanthroline)ruthenium(II) complexes), Δ- or Λ-[Ru(phen)3]2+. A racemic coordinatively unsaturated cyclometalated iridium(III) complex, rac-[Ir(nBuBQ)2Cl] (nBuBQH = 2butylbenzo[h]quinoline), was introduced into a short chromatographic column (1 cm × 0.4 cm (i.d.)) packed with a synthetic hectorite/Δ-[Ru(phen)3]2+ ion-exchange adduct. The adsorbed iridium complex was quantitatively retained within the clay interlayer and could not be eluted with methanol. Subsequent injection of the chelating ligand, disodium 4,7-diphenyl-1,10-phenanthrolinedisulfonate (Na2BPS), triggered coordination-sphere expansion, affording the anionic six-coordinate complex, [Ir(nBuBQ)2(BPS)]-, with a recovery yield of 88%. In contrast, the isolated Δ- and Λ-enantiomers of [Ir(nBuBQ)2Cl] exhibited substantially lower recovery yields of only 10% and 15%, respectively, indicating a pronounced chirality-dependent reaction pathway within the chiral clay environments.

Controlling the spatial distribution of photoluminescent molecules within constrained microenvironments remains a fundamental challenge in enhancing their photophysical properties. Herein, we demonstrate that the differential adsorption behaviors of enantiopure and racemic octahedral iridium(III) complexes on clay nanosheets can be exploited to modulate their photophysical and chiroptical properties, particularly circularly polarized luminescence (CPL). Two structurally related chiral complexes, [Ir(ppy) ₂ (phen)](PF ₆ ) ( Ir1-PF ₆ ) and [Ir(piq) ₂ (phen)](PF ₆ ) ( Ir2-PF ₆ ), were investigated. Upon adsorption onto colloidal clay, the pseudo- C ₃ -symmetric Ir1 ⁺ cation exhibited UV–vis, photoluminescence (PL), and electronic circular dichroism (ECD) spectra distinctly different from those in solution, a phenomenon absent for the sterically bulkier Ir2 ⁺ complex. Crucially, Ir1 ⁺ displayed distinct photophysical properties between its enantiopure and racemic forms, stemming from contrasting, optical-purity-dependent packing modes. While the racemate was proposed to form stable heterochiral pairs irrespective of loading density, the enantiopure complex underwent dense packing and concentration quenching at higher loadings. Furthermore, despite having the same absolute configuration, Ir1 ⁺ and Ir2 ⁺ exhibited opposite CPL signs in solution—an inversion computationally attributed to ligand-dependent changes in orbital topologies. Upon confinement within the clay matrix, the CPL intensity of enantiopure Ir1 ⁺ was significantly amplified, whereas that of Ir2 ⁺ decreased. This enhancement of the CPL intensity of Ir1 ⁺ upon clay adsorption closely parallels the effects of cryogenic cooling. Furthermore, molecular dynamics (MD) simulations revealed that, although both Ir1 ⁺ and Ir2 ⁺ adsorb onto the clay, Ir1 ⁺ adsorbs at a position closer to the clay surface and, relative to Ir2 ⁺ , tends to direct part of its ligands toward the hexagonal cavities of the clay surface; that strong interactions operate between the opposite-handed enantiomers of the racemate in both cases; and that the bulkier Ir2 ⁺ experiences weaker electrostatic repulsion and thus tends to aggregate—observations that were consistent with the experimental results. These findings establish clay nanosheets as powerful structural scaffolds for transforming weakly emissive molecules into highly functional chiral luminescent materials.

Cyclometalated iridium(III) complexes can possess Δ/Λ chirality and incorporate chiral ligands, enabling diverse photochemical applications, including sensing and asymmetric catalysis. Herein, two series of chiral iridium(III) complexes with or without a butyl group in their cyclometalated ligand framework were synthesised and characterised to clarify the role of the ligand framework in modulating the effects of Δ/Λ and ligand chirality on luminescence properties. The complexes were prepared by reacting enantiopure Δ- or Λ-[Ir( ⁿ BuBQ) ₂ Cl] ( 1 ; ⁿ BuBQ = monodeprotonated 2-butyl-benzo[ h ]quinoline) and racemic [Ir(HBQ) ₂ (CH ₃ CN) ₂ ]PF ₆ ( 2 ; HBQ = monodeprotonated benzo[ h ]quinoline) with d - or l -serine. Precursor 1 exhibited higher substitutional lability than precursor 2 under comparable conditions because of its coordinatively unsaturated five-coordinate structure. Each precursor yielded four enantiomerically pure stereoisomers—Δ 1 - d , Λ 1 - d , Δ 1 - l , and Λ 1 - l ( 1 -series) and Δ 2 - d , Λ 2 - d , Δ 2 - l , and Λ 2 - l ( 2 -series)—enabling the systematic isolation and comparison of all possible stereoisomers in each series. Molecular structure analysis by single-crystal X-ray crystallography and theoretical calculations suggest intramolecular interactions between the serine ligand and ⁿ BuBQ framework in the 1 -series. In dichloromethane, the diastereomeric sets in the 1 -series ( i.e. , Δ 1 - d /Λ 1 - l and Λ 1 - d /Δ 1 - l ) showed much larger differences in emission intensity and radiative rate constant than those in the 2 -series. These results suggest that the butyl group in the ligand framework influences how differences arising from the combination of Δ/Λ chirality and d / l configuration of the coordinated serine ligand are manifested in the luminescence properties of the complexes. This work may provide a useful guideline for the ligand framework design toward selective luminescence sensing of d -serine.

Cyclometalated iridium(III) complexes can possess Δ/Λ chirality and incorporate chiral ligands, enabling diverse photochemical applications, including sensing and asymmetric catalysis. Herein, two series of chiral iridium(III) complexes with or without a butyl group in their cyclometalated ligand framework were synthesised and characterised to clarify the role of the ligand framework in modulating the effects of Δ/Λ and ligand chirality on luminescence properties. The complexes were prepared by reacting enantiopure Δ- or Λ-[Ir( ⁿ BuBQ) ₂ Cl] ( 1 ; ⁿ BuBQ = monodeprotonated 2-butyl-benzo[ h ]quinoline) and racemic [Ir(HBQ) ₂ (CH ₃ CN) ₂ ]PF ₆ ( 2 ; HBQ = monodeprotonated benzo[ h ]quinoline) with d - or l -serine. Precursor 1 exhibited higher substitutional lability than precursor 2 under comparable conditions because of its coordinatively unsaturated five-coordinate structure. Each precursor yielded four enantiomerically pure stereoisomers—Δ 1 - d , Λ 1 - d , Δ 1 - l , and Λ 1 - l ( 1 -series) and Δ 2 - d , Λ 2 - d , Δ 2 - l , and Λ 2 - l ( 2 -series)—enabling the systematic isolation and comparison of all possible stereoisomers in each series. Molecular structure analysis by single-crystal X-ray crystallography and theoretical calculations suggest intramolecular interactions between the serine ligand and ⁿ BuBQ framework in the 1 -series. In dichloromethane, the diastereomeric sets in the 1 -series ( i.e. , Δ 1 - d /Λ 1 - l and Λ 1 - d /Δ 1 - l ) showed much larger differences in emission intensity and radiative rate constant than those in the 2 -series. These results suggest that the butyl group in the ligand framework influences how differences arising from the combination of Δ/Λ chirality and d / l configuration of the coordinated serine ligand are manifested in the luminescence properties of the complexes. This work may provide a useful guideline for the ligand framework design toward selective luminescence sensing of d -serine.

Controlling the spatial distribution of photoluminescent molecules within constrained microenvironments remains a fundamental challenge in enhancing their photophysical properties. Herein, we demonstrate that the differential adsorption behaviors of enantiopure and racemic octahedral iridium(III) complexes on clay nanosheets can be exploited to modulate their photophysical and chiroptical properties, particularly circularly polarized luminescence (CPL). Two structurally related chiral complexes, [Ir(ppy) ₂ (phen)](PF ₆ ) ( Ir1-PF ₆ ) and [Ir(piq) ₂ (phen)](PF ₆ ) ( Ir2-PF ₆ ), were investigated. Upon adsorption onto colloidal clay, the pseudo- C ₃ -symmetric Ir1 ⁺ cation exhibited UV–vis, photoluminescence (PL), and electronic circular dichroism (ECD) spectra distinctly different from those in solution, a phenomenon absent for the sterically bulkier Ir2 ⁺ complex. This spectral modulation is attributed to a precise size match between the Ir1 ⁺ ligands and the hexagonal cavities of the clay surface, leading to conformational locking that effectively suppresses nonradiative decay. Crucially, Ir1 ⁺ displayed distinct photophysical properties between its enantiopure and racemic forms, stemming from contrasting, optical-purity-dependent packing modes. While the racemate was proposed to form stable heterochiral pairs irrespective of loading density, the enantiopure complex underwent dense packing and concentration quenching at higher loadings. Furthermore, despite having the same absolute configuration, Ir1 ⁺ and Ir2 ⁺ exhibited opposite CPL signs in solution—an inversion computationally attributed to ligand-dependent changes in orbital topologies. Upon confinement within the clay matrix, the CPL intensity of enantiopure Ir1 ⁺ was significantly amplified, whereas that of Ir2 ⁺ decreased. This enhancement of the CPL intensity of Ir1 ⁺ upon clay adsorption closely parallels the effects of cryogenic cooling. These findings establish clay nanosheets as powerful structural scaffolds for transforming weakly emissive molecules into highly functional chiral luminescent materials.

Controlling the spatial distribution of energy donors and acceptors within constrained microenvironments remains a fundamental challenge in the development of efficient triplet–triplet annihilation upconversion (TTA-UC) and advanced photofunctional materials. Herein, we report the rational modulation of TTA-UC in an R-limonene-swollen organoclay (Sumecton-SAN) system using four iridium(III) complexes as donors: two cationic species, [Ir(ppy) ₂ (phen)]PF ₆ ( Ir1-PF ₆ ) and [Ir(piq) ₂ (phen)]PF ₆ ( Ir2-PF ₆ ), and two neutral analogues, [Ir(ppy) ₂ (acac)] ( Ir3 ) and [Ir(piq) ₂ (acac)] ( Ir4 ). We initially demonstrate that cationic Ir(III) sensitizers suffer from severe UC quenching in clay colloids due to spatial segregation; specifically, the cationic donors are electrostatically anchored to the polar clay surface via ion exchange, while the hydrophobic 9,10-diphenylanthracene (DPA) acceptors preferentially partition into the R-limonene-rich, hydrophobic interlayer domains. To overcome this microenvironmental mismatch, we employed the neutral Ir(III) complexes Ir3 and Ir4 . In these neutral systems, UC emission was significantly enhanced when the iridium complexes were loaded at a low density (corresponding to 5% of the cation exchange capacity (CEC) of the clay). Conversely, at a higher loading density corresponding to 50% of the CEC, Ir3 exhibited a marked decrease in UC emission, whereas the sterically bulkier Ir4 sustained its enhanced emission compared to the clay-free homogeneous solution. We attribute this difference to the aggregation-induced self-quenching of Ir3 on the clay surface at high concentrations, which was effectively suppressed by the steric hindrance of Ir4 . Furthermore, excited-state lifetime measurements of Ir2-PF ₆ and Ir4 in the presence and absence of the clay revealed contrasting behavior: the lifetime of Ir2-PF ₆ was shortened (the excited state of Ir2 ⁺ was destabilized) in the presence of the clay, whereas that of Ir4 was prolonged (the excited state of Ir4 was stabilized). These results suggest that both the neutral iridium donors and the DPA acceptors co-localize on the organically modified hydrophobic clay surfaces. Consequently, their molecular diffusion is effectively restricted to two dimensions, leading to amplified UC emission compared to that in a homogeneous solution. Based on these findings, we highlight the crucial role of tailoring the hydrophobic microenvironment on 2D clay sheet surfaces to facilitate efficient TTA-UC.

A single helicoidal microtrichium (approximately 10 µm in diameter and 100 µm in length) located at the edge of a European hornet hindwing was studied by using microscopic infrared spectroscopy, leading to the conclusion that it contained proteins in the β-sheet as a main component. No difference was deduced between the left and right wings.

Controlling the spatial distribution of photoluminescent molecules within constrained microenvironments remains a fundamental challenge for enhancing their photophysical properties. Herein, we focus on the differential adsorption behaviors of enantiopure and racemic octahedral metal complexes on clay surfaces as a means to amplify these properties, including circularly polarized luminescence (CPL). Two iridium(III) complexes exhibiting Δ and Λ chirality, [Ir(ppy) ₂ (phen)](PF ₆ ) ( Ir1-PF ₆ ) and [Ir(piq) ₂ (phen)](PF ₆ ) ( Ir2-PF ₆ ), were employed as chiral luminophores. Investigations into the adsorption behavior of these complexes on colloidal clay revealed that the Ir1 ⁺ cation, which possesses pseudo- C ₃ symmetry, displays UV–vis, photoluminescence (PL), and circular dichroism (CD) spectra distinctly different from those of the free complex in solution. Conversely, no such spectral changes were observed for the bulkier and lower-symmetry Ir2 ⁺ complex in the clay colloidal suspensions. These spectral changes in Ir1 ⁺ are attributed to its conformational fixation on the clay surface and the restricted molecular motion, which effectively suppress nonradiative decay processes. Specifically, structural matching between the ligands of Ir1 ⁺ and the hexagonal cavities of the clay surface likely leads to rigid stabilization. In contrast, the bulkier ligands of I Ir2 ⁺ likely prevent such rigid fixation. Furthermore, Ir1-PF ₆ and Ir2-PF ₆ with the same absolute configuration (Δ or Λ) exhibited opposite CPL signs in solution. This inversion is attributed to the ligand-dependent changes in orbital topologies, which reverse the transition dipole moments. In colloidal suspensions, the CPL intensity of Ir1 ⁺ increased—an effect similarly attributed to conformational fixation—whereas that of Ir2 ⁺ decreased. Remarkably, this enhancement of CPL intensity of Ir1 ⁺ upon clay adsorption is highly reminiscent of cryogenic cooling. These results demonstrate that utilizing clay nanosheets as structural scaffolds is a powerful strategy for transforming molecules with weak inherent chiroptical properties into highly functional chiral luminescent materials.